It is now a very old joke but I do recall the first time I heard it used was in my RAF training days (1963) when several of us were wandering back to our billets from the NAAFI and we noticed one of the RAF Police team still working out. This guy was a total fitness freak and he was given to running around the camp, stopping at intervals to do 30 or so press ups and then sprinting on again.
Anyway he was at one of his press up stages as we drew level with him and a broad Scottish accent from within our ranks bellowed "I dinnea like tae tell ye laddie but yon lass has given up and gone hame".
To a dozen or so young erks this was the funniest thing we had ever heard ~ particularly directed at one of the hated "Snowdrops".